Permeable refractory products

ABSTRACT

A porous refractory body, primarily a porous plug for the refractory lining of a vessel containing molten metal through which plug gas can be blown into the metal. This body has a cold crushing strength of not less than 200 kg/cm2 and consists of a coarse-grained refractory material with a minimum quantity of a suitable binding agent, and has permeable pores of a cross section not less than 0.05 mm and a gas permeability of at least 100, and preferably more than 500 nanoperm. The hot bending strength or modulus of rupture of the body at 1,400* C is from 20 - 60 kg/cm2. The refractory material is mixed with the binding agent, and the mixture is compressed with a pressure of at least 300 kg/cm2 before firing to bring substantially all of the grains into contact with adjacent grains.

United States Patent [191 Koerner n11 3,753,746 Aug. 21, 1973 PERMEABLE REFRACTORY PRODUCTS 211 Appl. No.: 106,709

Related [1.8. Application Data [63] Continuation-in-part of Ser. No. 676,061, Oct. 18,

1967, abandoned.

[30] Foreign Application Priority Data Oct. 19, 1966 Great Britain 46,850/66 [52] [1.8. CI 106/58, 106/40 R, 106/65, 106/67 [51] Int. Cl C041) 35/04 [58] Field of Search 106/57, 58, 65, 67, 106/40 [56] References Cited UNITED STATES PATENTS 2,007,052 7/1935 Howe 106/67 FOREIGN PATENTS OR APPLICATIONS 714,478 7/l965 Canada 106/57 Primary Examiner-James E. Poer Attorney-Brumbaugh, Graves, Donohue & Raymond [57] ABSTRACT A porous refractory body, primarily a porous plug for the refractory lining of a vessel containing molten metalthrough which plug gas can be blowninto the metal. This body has a cold crushing strength of not less than 200 kg/cm and consists of a coarse-grained refractory material with a minimum quantity of a suitable binding agent, and has permeable pores of a cross section not less than 0.05 mm and a gas permeability of at least 100, and preferably more than 500nanoperm. The hot bending strength or modulus of rupture of the body at 1,400 C is from 20 60 kg/cm". The refractory material is mixed with the binding agent, and the mixture is compressed with a pressure of at least 300 leg/cm before firing to bring substantially all of the grains into contact with adjacent grains.

10 Claims, 2 Drawing Figures 7 PAIENIEBmzu ma INVENTOR. OTTO KOERNER BY mm...

A TTORNEYS his PERMEABLE REFRACTORY PRODUCTS measured in nanoperm. One nanoperm equals 10 This is a continuation-in-part of my copending US. perm. A permeability of l perm is defined by a flow Application Ser. No. 676,061, filed Oct. 18, 1967, now volume of 1 cc per cm per second through a permeaband fi able body of 1 cm thickness under a pressure of l dyne BACKGROUND OF THE INVENTION per cm for a fluid having a viscosity of l poise.

Four different mixtures were prepared according to This invention relates to high strength refractory the following table which also records all the relevant bricks, blocks, plugs and the like which are also highly test results; permeable to the passage of gases and vapors and to methods of manufacturing such refractory products. TABLET n l Such products in the form of plugs are, for example, Mixture- 1 2 3 4 used to blow gases under pressure into vessels containcorundum (percent), ing molten metals and, in particular, into molten steel 50 50 0.5-1 mm. grain size 50 50 for the purpose of agitating the liquid metal and remov Binder material +5 +5 +10 +10 ing undesirable impurities from it, or for providing an g g'a g gg -5555 3;; +2 +2 +3 +3 efficient reaction between the small gas bubbles and (p 2-3 mm 6 13 1 9 the molten metal. 1-2 mm.. 43 7s 41 rs The above object could, however, not be attained in 8:85;? 2 2 a satisfactory manner before the present invention. BelQW 5 5 9 9 Properties of refractory body: Known refractory products with a high permeability to Linear expansion during firing gases were mechanically we week to Stand up to the iiiiiiiifiityfjjjjjjjjiij:13: II 3122 323 322? severe conditions of a high temperature metal bath. On p i a i Total porosity (percent). .1 37.2 33.!) 35.7 the other hand, refractory products having sufficient Permeability (nanoperm) 1,220 350 1,210 960 mechanical strength and resistance to chemical attack 580 m were not sufficiently permeable to gases. Q2 pig 8;; g g As described in detail hereinafter, the porous refracn i 1 I i 1 i I tory body of the present invention has a combination ir fffgg gggi f {ggfgfi gi ggggggm fg gg of greater mechanical strength and greater permeability to gases than the porous refractory bodies of the Th bl h ws that th four samples h ve suit ble P such as those descl'lbed, for p In the porosity and crushing strength but none of them exhib- U- 3- Pat. (0 Howe, and m the its the hot bending strength (modules of rupture) at to Langrod, NO. 3, high temperature which is required for porous refrac- Examples 1 and 2 give bekfw Illustrate the P p tory materials used for permeable plugs. As shown in ties of prior art refractory bodies manufactured in acbl I, the bending strength f the Howe material is cordance with the Howe and Langrod patent disclo- 5 din l low at 1,200 C and zero at 1,400 C. Sure-5, respectlvelylt will be seen that the cold crushing strength is higher for the samples with the higher content of binder Example material. On the other hand, the samples containing the 'g corundum with gram slzes ofo-l to 0.5 to 1 mm corundum fraction have the higher perme- 1 mm and l to 2 mm was used as the refractory mateabimy. rial to insure g Permeability in the refractory y The overall result is thatall four samples would be formed the e o totally unsuitable for use as permeable bricks in vessels The binder material used consisted of a clay relacontaining "when l,

tively low in alumina mixed with another clay relatively high in its iron oxide content (so-called Engobe Clay) Example 2 and with small additions of CaO, MgO and alkali. This The preparation of a refractory material, according mixture gives a chemical composition which is quite to the Langrod specification, and results of the fired similar to the one mentionedby Howe on page 2, right specimens are given below:

column, lines to 65, as is shown by the following ta- Mixture:

ble: 50 percent by weight calcined alumina (calcined at SiOg A130 F920 MgO C N320 K20 TiO Blhdtl'llltllflltlltltf'Ol'dllli!l0 Howe 64.3 19.3 4.6 2.1 3.7 .3 3.8 0.9 Bindur nintvrialuscdiu comparison tests 67 19 5. 0 2. 2 3. 7 2 3. 6 1. 1

The refractoriness of the Howe test binder material 1,200" C), substantially over 200 mesh size (0.074 corresponded to Seger Cone l6 (firing temperature of L4450C) The corundum mammal was mlxed 5 or 20 percent by weight calcined alumina milled with 10 percent (by weight) of the binder material and the usual addition of water. The mass was pressed under a 65 pressure of 200 kg/cm, was dried and was finally fired at l,300 C for a period of 4 hours. The gas permeabilpa ation of Refractory ity (as defined by German Standard DIN 51058) was The mixture was compressed into samples X 60 water in the form of a slurry in a ball mill for I2 hours.

Firing shrinkage 4% linear Bulk density 2.34 g/cm Specific gravity 3.96 Porosity about 40% Permeability 0.3 nanoperm Permeable pore size (determined by the method of Washbum) Cold crushing strength below 0.003 mm 990 kg/cm It can be seen that although the porosity of the Langrod specimens was high, the gas permeability was extremely low so as to make them completely useless for gas blowing. The relatively high firing shrinkage was detrimental to the production of alumina refractory bricks.

It is an object of the present invention to overcome the shortcomings of the refractory bodies of the prior art.

SUMMARY OF THE INVENTION The present invention provides a porous refractory body having a high bending strength as well as a high porosity. More particularly, the body has a cold crushing strength of not less than 200 kg/cm comprising a coarse grained refractory material sintered with a minimum quantity of a suitable binding agent. The body has permeable pores of a cross section of not less than 0.05 mm and a gas permeability of at least 100 and preferably more than 500 nanoperm (npm). The hot bending strength, or modulus of rupture, of the body at l,400 C is at least 20 30 kg/cm. When materials rich in aluminum oxide are used to form the refractory body, as will be described below, the modulus of rupture is about 50 6O kg/em at 1,400 C.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate how a typical porous refractory body according to the present invention may be used.

FIG. 1 shows schematically the introduction of argon or other gas into a ladle containing a molten metal through the porous refractory body of the present invention; and

FIG. 2 is an enlarged schematic view of the portion of the ladle of FIG. 1 which holds the porous refractory body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment, the coarse-grained refractory material of the present invention is a refractory oxide-containing material having at least 85 percent by weight of grain sizes of more than 0.5 mm with an addition of less than 10 percent by weight of a suitable refractory oxide-containing binding agent. To assure the advantage of the present invention, it is important that at least 30 percent of the binder comprises the same oxide mainly constituting the refractory material. For the purpose of introducing gases or vapors into molten metals the permeable pores should have an average cross section of 0.1 to 0.2 mm and a volume of 10 to 15 percent (as determined by the method of Washburn). It will be appreciated that the volume of the permeable pores may be only a fraction of the total porosity of such a body. Substantially all the grains in the body are in physical contact with, and are supported by, the surfaces of adjacent grains and the sintered binding agent joins the adjacent grains about their areas of contact while forming permeable pores between the grains.

The oxide-containing refractory body includes bricks, blocks, plugs, whether formed and fired at the factory or in situ. The materials preferably used in forming such bodies are refractory dead-burned (or fused) and coarse-grained neutral refractory substances, such as mullite and corundum, which are rich in aluminum oxide (alumina), or basic refractory materials, such as magnesia (magnesite).

The oxide-containing binding agent is a material having a refractory component which is used to join the refractory particles at their points or areas of contact. Binding agents preferably used in conjunction with the refractory granular materials rich in aluminum oxide (e.g., mullite and corundum) used in the present invention are refractory clays having a high aluminum oxide content. Finely dispersed alumina and water-soluble alumina, with or without the addition of clay, finely dispersed ceramic slurry of mullite, along with additions of a bond-activating agent, such as monoaluminum phosphate or chromium aluminum phosphate, also may be used. The latter two materials are preferably used together with alumina. When a basic refractory material,'such as sintered magnesia, is used to form the refractory body, finely dispersed magnesia or causticburned magnesia is the binding agent with additions of small amounts of a bond-activating agent, such as finely grained chrome ore, the sesquioxides (e.g., Fe,o,, Al- 0 and C50 chrome salts, chromic acid or 8,0,.

The binding agent is preferably composed of two essential components. The first is a highly refractory component comprising an oxide, such as alumina or magnesia, which is the same oxide mainly contained in the coarse-grained refractory material chosen. The second is a bond-activating agent, such as aluminum monophosphate, boric acid or iron oxide, etc., as set forth above. The ratio of refractory part to bond-activating agent is at least about 2:1. In other words, at least about 30 percent of the binding agent is the same oxide as that mainly contained in the refractory material.

Before firing, the formed bricks are compacted by subjecting them to a pressure of at least 300 kg/cm and preferably more than 500 kg/cm to force the grains into particleto-particle contact. Accordingly, when the above-mentioned refractory materials and their binding agents are fired to form a porous refractory body, substantially all of the grains of the refractory material are supported by and are in contact with adjacent grains and their contact points are embedded in bridges of crystalline sintered material. It will be apparent that the high temperature bending strength of these sintered contact areas is mainly influenced by the character of the binding agents and the firing temperature. The use of refractory dead-burned and coarse-grained materials in predominant amounts in conjunction with a high degree of compression insures that the bodies have only a small burn shrinkage and that they are closely sized.

The following examples illustrate how refractory bodies having these characteristics can be manufactured in accordance with the present invention: Example 3 (Porous Plug for Steel Casting Ladles) Raw Material: Sintered mullite having the following granulation:

2.5 to 3.0 mm 20% by wt. 2.0 to 2.5 mm 20% by wt. 1.5 to 2.0 mm 18% by wt. 1.0 to 1.5 mm 17% by wt. 0.5 to 1.0 mm 15% by wt. 0.0 to 0.5 mm by wt.

Permeability 400 npm Open pore volume 10% to Cold crushing strength 400 kg/cm Hot bending strength (or Modulus of Rupture) 63 kg/cm at and 56 kg/cm at Example 4 (Permeable Block for Use in Converters) Raw Material: Sintered magnesia (0.3 percent Fe O of the following granulation:

3.0 to 4.0 mm 4% by wt. 2.0 to 3.0 mm 24% by wt. 1.0 to 2.0 mm 34% by wt. 0.5 to 1.0 mm 27% by wt. 0.0 to 0.5 mm 11% by wt.

Binding Agents:

a. Caustic magnesia b. Boric acid 0.2 0.5 percent by wt. and/or c. lron oxide 0.2 percent 1.0 percent by wt. The magnesia is mixed with the sintering agents in the conventional manner. The mixture is formed into blocks under a pressure of 900 kg/cm and fired at 1,750 C.

The resulting physical properties of the block are:

3 percent by wt.

Permeability Cold crushing strength 1080 npm 400 kg/cm The hot bending strength of the permeable block made without the addition of boric acid is comparable to the strength of the plug manufactured according to Example 3.

Example 5 (Porous Brick for Casting Ladles) Raw Material: Corundum with a grain size range of either 0.5 to 3 mm or 1 to 3 mm Binding Agents:

a. Clay containing not less than 43 percent A1 0 (grain size of up to 0.25 mm) 5 percent by wt.

b. Aluminum monophosphate (in the form of a 50 percent aqueous solution): 1.5 percent by wt. The mixture is pressedat a pressure of 500 to 600 kg/cm and fired for not less than 4 hours at a temperature of about l,600 C.

The resulting physical properties are:

Permeability 500 to 700 npm Cold crushing strength 250 to 350 kg/cm The hot bending strength is comparable to that of the plug manufactured according to Example 3.

Porous plugs according to Example 3 are suitable for flushing steel with argon in casting ladles prior to. casting. One or more plugs are arranged within the refractory lining at the bottom of the ladlle. These ladles contain up to 300 tons of steel, and 2 to 6 m of argon per ton may be used in the process which should not last longer than 10 minutes. This short time for the process is possible because a large volume of small gas bubbles can flush the liquid steel due to the highly permeable plugs. The agitation is strong enough to homogenize the molten metal in the ladle as well as equalize the temperature at various points in the molten metal. On the other hand, the upward momentum of the small gas bubbles is not strong enough to prevent a clean separa tion of slag and metal.

Porous blocks according to Example 4 are suitable for blowing oxygen and other gases into the molten pig iron of converters. Due to the high permeability of the block, oxygen can be blown at a sufficiently high volu-' metric rate so that a high quality output is maintained. The metallurgical reactions are much more efficient due to the very large surface of contact between the gas and metal and to the longer period of contact between them. Due to the very high refractoriness and mechanical strength of the blocks as well as the great evenness of the gas flow, the life of such blocks is very satisfactory.

It will be appreciated that the pore size of the body of the present invention can be adjustedv according to the purpose for which it is used by varying the particle size of the granulated raw material. But in each case it is advantageous to exclude as far as possible grains below 0.05 mm and to use the smallest possible amount of binding or sintering agent. It has: been found that this amount should be, if possible, less than about 5 percent but not less than about 3 percent.

For a given granular material of a given size range the relation between strength and permeability of the body formed by the present invention may be adjusted by varying the pressure with which the mixture is compacted prior to firing. By the way of example, the following variations may be obtained:

Compacting pressure (kg/cm) 300 600 1000 Cold crushing strength of fired brick (kg/cm) 200 400 500 Permeability (nanoperm) 1000 400 It is also possible to vary the particle size in the direction of the intended gas flow by adding several successive layers of increasing or decreasing particle size into the press mould. 1f the largest size is provided at the top, i.e., at the face to be in contact with the metal, this may improve permeability under actual conditions where the temperature of the gas increases during its passage through the porous material, and both its volume and viscosity increase substantially.

In the same way it is possible to improve the refractoriness and chemical resistance of the plug or block by using for the top layer a different material of exceptional quality.

FIGS. 1 and 2 show the use of the porous refractory body of the present invention. FIG. 1 illustrates the introduction of argon gas into a casting ladle which contains molten metal 11 through a porous refractory plug 12 in accordance with the invention. The gas is supplied to the ladle from a container 13 through a connecting pipe 14, three control valves l5, l6 and 17, and a flow meter 18. The porous refractory body 12 of the present invention is positioned at the bottom of the ladle 10 at the end of the pipe 14 so that the gas diffuses through it into the molten metal 11.

FIG. 2 is an enlarged view of the construction of the porous plug formed by the body of the invention. The porous refractory body 12 is placed in the refractory lining 19 of the ladle 10 which has a metal casing 20. In the illustrated embodiment, the porous body 12 is supported on a refractory base 21 and comprises three layers 22, 23 and 24, having progressively greater gas permeability. For this purpose, the layers are made with successively greater grain size so that the average grain size of the granular refractory material of the entire body 12 increases in one direction through the body. A refractory spacer 25 also supports a portion of refractory body 12. In operation, gas is fed through a pipe 14 into a pressure balancing chamber 26 located below the lining and thence through the body into the ladle l0.

The refractory body according to the present invention therefore provides a strong porous plug, capable of withstanding the high temperature and pressure of molten metal while permitting gas to be blown into the metal from the bottom of the vessel containing the metal.

I claim:

1. A method for manufacturing a high strength porous refractory body comprising compressing a mixture which consists essentially of a granular material selected from the group consisting of oxide containing neutral and oxide containing basic refractory materials, said granular materials having at least 85 percent by weight of grains with a size of at least 0.5 mm, and no more than about l0 percent by weight of a refractory binder material which consists essentially of a refractory oxide component and a bond-activating agent component by applying thereto a pressure of at least 300 kg/cm so as to control the permeability and strength of the resulting body, and sintering the mixture by firing the body at a high temperature to produce a refractory body having a cold crushing strength of no less than 200 kg/cm a permeability of at least 100 nanoperm and a modulus of rupture of a greater than about 20 kg/cm at l,400 C.

2. A method according to claim 1 including the step of compressing the mixture by applying pressure such as to produce a refractory body having permeable pores with an average pore size of about 0.l to 0.2 mm and a volume of about 10 percent to 15 percent of the body volume as measured by the Washburn method.

3. A method according to claim 1 wherein the granular material is selected from the group consisting of mullite, magnesia and corundum.

4. A method according to claim 1 wherein the binder includes a material selected from the group consisting of alumina and magnesia.

S. A method according to claim 1 wherein the granular material is selected from the group consisting of mullite and corundum, the binder is a material comprising aluminum oxide, and the bond-activating agent is selected from the group consisting of monoaluminum phosphate and chromium aluminum phosphate.

6. A method according to claim 1 wherein the granular material and binder comprise magnesia, the bondactivating agent is selected from the group consisting of chrome ore, the sesquioxides; chrome salts, chromic acid and boric acid.

7. A porous refractory body comprising at least about 90 percent by weight of a granular refractory material selected from the group consisting of oxide-containing neutral and oxide-containing basic refractory materials, at least about percent by weight of the granular material having grain size greater than about one-half millimeter, substantially all of the grains being in physical contact with, and supported by, the surfaces of adjacent grains, and a sintered binding agent joining the adjacent grains of the body at their areas of contact and providing permeable pores therein having an average size of at least about 0.05 millimeter and a total volume of not less than about 10 percent of the body volume as measured by the Washburn method, at least about 30 percent of the binder agent comprising the same oxide mainly constituting the granular refractory material, whereby the body has a modulus of rupture of at least 20 ltg/cm at I,400 C, a cold crushing strength of at least 200 lag/cm and a permeability of at least I00 nanoperm.

8. A porous refractory body according to claim 7 comprising a plurality of successive layers having increasing particle size. 7

9. A porous refractory body according to claim 7 having a gas permeability of at least about 500 nanoperm.

10. A porous refractory body according to claim 7 wherein the granular refractory material is selected from the group consisting of mullite and corundum and the binding agent comprising refractory clay containing at least about 43 percent A1 0 STATES PATENT OFFICE CERTIFICATE OF CORRECTIQN Patent No.. 3,753,746 Dated August 21, 1973 Inventofls) Otto Koerner It is certified that error appears in' the aboveidentified patent and that said Letters Patent are hereby corrected as shown below: i b

On the title page, the identification of the Inventor [76] "Rothstrasse 1062, Wiesbaden, Germany" should read H Rothstrasse 10, 62 Wiesbaden, Germany Column 1, line 51,

TiO should'read TiO Column 2, line 25, "9" should be 5 C l n 8, line 55; "comprising should be comprises Signed and sealed this 29th day of January 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. RENE D. TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM PO-1OSO (10 69) USCOMMDC wands i: U. 54 GOVERNMENT PRINTING OFFICE 19.9 0-3G6-33L 

2. A method according to claim 1 including the step of compressing the mixture by applying pressure such as to produce a refractory body having permeable pores with an average pore size of about 0.1 to 0.2 mm and a volume of about 10 percent to 15 percent of the body volume as measured by the Washburn method.
 3. A method according to claim 1 wherein the granular material is selected from the group consisting of mullite, magnesia and corundum.
 4. A method according to claim 1 wherein the binder includes a material selected from the group consisting of alumina and magnesia.
 5. A method according to claim 1 wherein the granular material is selected from the group consisting of mullite and corundum, the binder is a material comprising aluminum oxide, and the bond-activating agent is selected from the group consisting of monoaluminum phosphate and chromium aluminum phosphate.
 6. A method according to claim 1 wherein the granular material and binder comprise magnesia, the bond-activating agent is selected from the group consisting of chrome ore, the sesquioxides; chrome salts, chromic acid and boric acid.
 7. A porous refractory body comprising at least about 90 percent by weight of a granular refractory material selected from the group consisting of oxide-containing neutral and oxide-containing basic refractory materials, at least about 85 percent by weight of the granular material having grain size greater than about one-half millimeter, substantially all of the grains being in physical contact with, and supported by, the surfaces of adjacent grains, and a sintered binding agent joining the adjacent grains of the body at their areas of contact and providing permeable pores therein having an average size of at least About 0.05 millimeter and a total volume of not less than about 10 percent of the body volume as measured by the Washburn method, at least about 30 percent of the binder agent comprising the same oxide mainly constituting the granular refractory material, whereby the body has a modulus of rupture of at least 20 kg/cm2 at 1,400* C, a cold crushing strength of at least 200 kg/cm2 and a permeability of at least 100 nanoperm.
 8. A porous refractory body according to claim 7 comprising a plurality of successive layers having increasing particle size.
 9. A porous refractory body according to claim 7 having a gas permeability of at least about 500 nanoperm.
 10. A porous refractory body according to claim 7 wherein the granular refractory material is selected from the group consisting of mullite and corundum and the binding agent comprising refractory clay containing at least about 43 percent Al2O3. 